Figuring out a gear's specifications from picture

[nnam]

I bought a J head Bridge port clone mill in a very bad shape, scrap metal price a while back. It was in such a bad shape that I was a bit embarrassed to share, until I can bring it back to life. However, I need help. There are various gears in the auto down feed assembly that are bad. So far, the input gears are bad, here's a listing that has the input shaft with 3 straight spur gears:

https://www.ebay.com/itm/Bridgeport...e-worm-gear-cradle-2190059-M1318/173988385261

Then, the cluster gear is also bad , here's a listing:

https://www.ebay.com/itm/Bridgeport...tomatic-Feed-Shaft-CNC-Mill-Tool/323966092106

So, I am thinking of making the gears, or bronze braze and cut it out, versus buying the parts, with buying as a last option, and saving the money for things like dividing head, which I would need in the future anyway.

What do you think? Will it be possible to take a picture of a good tooth, zoom it large and some how match with various profile of teeth (from generated calculator for example) and figuring out various thing like pressure angle, diametral pitch, etc. Or maybe since it's a bridge port clone,they're well known values (I couldn't find it anywhere). I even wonder if the 3 gears (of the cluster gears) has a same specs such as diametral pitch and pressure angle.

 

[nnam]

Doing some more homework on these, here's what I found so far:


1. The diametral pitch is 20 for all these gears. This translates to the modulus of 1.27.

(large, medium and small)

For those interested in numbers, here are what they are:

OD for each gears: 1.5", 1.2", 0.95"

Teeth count TC: 28, 22, 17

Using formula PD = OD/(2/TC + 1), we have for each:

PD = 1.4", 1.1", 0.85"

Cir pitch = PD * pi / TC = 0.1570795 (for all 3)

Diametral pitch = pi / cir pitch = pi / 0.1570795 = 20

2. Pitch angle

How to Measure Pressure Angle of a Gear – Gear Pressure Angle, Gear Terminologies, Equations

In this gear design article will discuss on how to measure pressure angle of a gear and the different gear terminologies and equations related to it.

www.brighthubengineering.com

BP = Base pitch = base diameter * pi/TC = 1.297 * 3.14159/28 = 0.145522937"

PA = pitch angle

BP = pi * cos(PA)/DP

PA = acos (BP * DP /pi) = acos(0.145522937×20÷3.14159) = 22.115233014

I am not 100% sure of my base pitch diameter measurement, but according to the above, it's 22 degree.

For the gear, base pitch can be a bit smaller value since the diameter is smaller than the diameter measured at the base of the teeth.
So, putting that into the equation above, the angle can be larger than 22, possibly 24 or 25.

I use this site to generate the gear just for visual comparison, looks pretty close:

http://hessmer.org/gears/InvoluteSpurGearBuilder.html

So any suggestion where to go next? Any correction to the calculation above would be appreciated.

I wonder if I mix 20 pitch angle (more available) with existing 25 (or whatever that is) would cause too much issue. Some said they replaced with "close" teeth and it worked good.

I also like to buy a set of cutters, and keep it for other cuts, so I would stick to "common" angle if possible.

 

[nnam]

Taken a picture and zoom in large, compared it with the generated image, and measure the tip, it appears the pressure angle is 14.5 degree.
I need this one works out.

 

[nnam]

Using measurement at the base of 2 teeth, then 3 teeth length difference, it's about 0.143, and the pressure angle is 24.4 degree.
Since it's small, if 0.145, then the value changes to 22.6 degree. This is for the 28 tooth gear.

For the 22 tooth, it's 0.148, shows 19.6 degree angle.

For 17 tooth gear, ranges from 0.145 to 0.147. At average of 0.146, the angle is 21.6483 degree.

So it's a bit all over places. For smaller gears, larger angle gives strength to the teeth. However, it's a bit louder and less smooth.
The smallest gear's teeth top surface appears much wider than the 28 tooth gear. Which means it should have larger angle, but the numbers just don't show a good pattern.

Maybe the gears are old, rusty. I may need to fill them all up with bronze and cut them all to a same angle again. I really don't like to do too much, and prefer to fix a few most bad teeth. Maybe I shouldn't be too worry about gear cutting.